The present invention generally concerns motion transmitting mechanism for use in copying machines of the type having a cam with a cylindrical cam surface, a feeler held against the cam surface, a work block movable in translation perpendicularly to the generatrices of the cam surface, and a hydraulic, mechanical, pneumatic or other transmission for moving the work block in dependence on the movements of the feeler; most often the work block is a tool-carrying block and this is able to produce a surface homologous, in practice homothetic, to the surface of the cam directing it.
A problem encountered with such machines is ensuring rapid adaptation to the reproduction of different surfaces.
This is particularly so in the case of copying machines for producing aspherical surfaces such as those of the moulds for making contact lenses.
In fact, to provide moulds for making contact lenses with different geometrical characteristics it must be possible to modify the profile of the cam directing the copying machine used.
To this end it is possible to provide as many cams with different profiles as there are types of surface to be obtained, and to fit the copying machine with the cam corresponding to each type of surface.
As well as calling for the manufacture and storage of a large number of different cams, and thus being costly, this solution requires on each occasion a lengthy and delicate cam fitting operation, due to the adjustments which are necessary.
To reduce this inconvenience it has already been proposed to use cams with variable profiles or cam surfaces which can, with the appropriate adjustments, be adapted to the various types of surface to be obtained, as for example in U.S. Pat. No. 3,881,378.
But in practice variable profile cams of this type which are currently available, while being particularly useful for surfaces with radii of curvature at the periphery which are greater than that at the centre, do not allow surfaces to be produced having radii of curvature at the periphery which are less than that at the centre.
Such surfaces may be needed, however, particularly for producing moulds for making contact lenses for correcting strong myopeia, with a view to decreasing the thickness of such a lens at the edge.